Asthma is a complex disease affecting an estimated 20.5 million Americans and costing the US approximately $16.1 billion annually in health care expenses.1 Models for predicting adult asthma proposed to date have been constructed using clinical characteristics. Measures that have been found to be significant independent predictors include lung function, airway hyperresponsiveness, atopy, parental history of asthma, and female gender.5, 6 Although a parental history has been found to be a predictor of asthma, genetic data have not been used to investigate this phenomenon.5 
Asthma results from the complex interaction of multiple genetic and environmental factors, which causes its phenotypic expression to vary across individuals. In genetic association studies, over 100 genes have been associated with asthma- and atopy-related phenotypes.7 Of these genes, 25 have been associated in six or more populations and 54 have been associated in two to five populations. None of the single-gene association studies to date has developed a reliable predictive model of asthma. Because asthma is a prototypical complex disease, traditional association studies, which attempt to find single gene associations or assume an additive model of gene interaction are inherently limited in finding complex genetic interactions that may be predictive of asthma.